Switching circuits



April 12, 1966 D. E. TYZACK 3,246,174

SWITCHING CIRCUITS Filed June 14, 1962 United States Patent G This invention relates to switching devices and especially to switching devices suitable for selectively connecting a voltage source to a utilisation circuit without the introduction of appreciable voltage errors.

In analogue computing circuits, and especially such circuits for positioning devices for the automatic control of machine tools it is frequently required to selectively connect one of a plurality of voltage sources to a comparison circuit and it is important that the connection should introduce little error into the voltage applied to the comparison circuit. This selective connection is usually achieved by sliding switches such as are used as uniselectors or by relay operated switches. In operation, however, such switches become unreliable as a result of wear due to one contact sliding over the other or as a result of surface deposits formed by corrosion.

It is an object of the present invention to avoid the above disadvantages.

According to the present invention there is provided a switching circuit comprising a tapped transformer winding, an output load having one terminal connected to one tapping of said winding and having a second terminal connected to ground, a plurality of transistors the emitter collector path of each of which is connected between a respective tapping of said winding and ground, and means for selectively switching one of said transistors to a state of high conductivity and for maintaining the rest of said transistors in a state of low conductivity, whereby different fractions of said winding may be selectively connected to said load.

In order that the invention may be fully understood and readily carried .into effect it will now be described with reference to the single figure of the accompanying drawing which represents one example of a switching circuit according to the invention.

Referring to the drawing, which shows an alternating voltage selector switch according to the invention, alternating voltage of, say 1000 c.p.s. from a reference source is applied to the terminals IN of the primary winding of the transformer T. The secondary winding of the transformer T has ten equally spaced output terminals a a a 11 Each one of the output terminals a a a a is connected to the emitter of a corresponding one of the transistors 1 t t t the collectors of which are connected to ground. The terminal a of the secondary winding of the transformer T is also connected to the output terminal OUT" between which and ground the utilisation circuit L for the selected alternating voltage is connected. The base electrode of each of the transistors 1 t t t, is connected via a resistor R to a source P of polarising voltage. A diode matrix DM interconnects the base leads of the transistors t With the output terminals of four triggers Q Q Q and 0 Each of the triggers Q Q Q and Q, is arranged to give two outputs in push-pull, so that if the trigger is in the "0 state the 0 output line is held at a negative potential with respect to ground and the "1" output line at a positive potential, and if the trigger is in the 1 state the 0 output line is positive and the 1 output line negative. The source P of polarising voltage provides a constant negative voltage with respect to ground and is sufiicient to bottom the transistors t in the absence of the effects of the diode matrix DM. However, the outputs of the triggers Q Q Q and Q, can act via the diodes of the matrix DM to raise the bases of the transistors t to a positive value sufficient to prevent conduction. The arrangement of the diodes in the matrix DM is such that if a binary coded number in the range 0 to 9 is stored in the triggers Q, with the digit of least significance in Q,, the next in Q and so on, then the voltage on the base of the transistor t having a suiiix equal to this number is allowed to be that of the suorce P so that the transistor is bottomed because all of the diodes connected to that base are connected from outputs of the triggers Q which are held at negative potentials whereas all the remaining transistors are held non-conducting as a result of current from one or more positive outputs of the triggers Q applied via diodes of the matrix DM to the bases of the transistors.

The voltage produced by the part of the secondary winding between a and the tapping connected to the conducting one of the transistors I therefore appears between the terminal OUT and ground for application to the utilisation device L.

Although in the example shown in the figure the collector electrodes of the transistors t are connected to ground and their emitters to the transformer secondary winding, they may also be connected with their emitters grounded and their collectors connected to the winding.

To prevent conduction of the transistors on the positive going peaks, with respect to ground, of the alternating voltage across the transistors it is necessary that the positive voltages applied to the bases of the transistors required to be nonconducting should be at least as large as the peak voltages across the transistors in order to prevent conduction. Therefore the polarising voltage from the source P should be as large as the single amplitude peak of the AC voltage produced across the secondary winding of the transformer T.

Another embodiment of the invention is a phase reversing switch for an A.C. signal in which the AC. signal is applied to the primary winding of a transformer having a centre-tapped secondary winding the end terminals of which are connected to ground via the collector-emitter paths of respective transistors. The desired output signal is derived from the centre tap of the secondary winding with reference to ground, the phase of the output signal being determined by which of the transistors is arranged to be conducting.

Although the switching circuit has been described in its application to a source of alternating voltage in the form of a transformer winding it is clear that it is equally applicable to any other floating voltage source. Furthermore, the switching voltages for the transistors may be derived from means other than a diode matrix, and in a particular application the switching voltages may be derived from a ring counter so that a predetermined succession of voltages is applied to the utilisation circuit.

What I claim is:

1. A switching circuit comprising a tapped transformer transistors the emitter collector path of each of which is connected directly from a respective tapping of said winding to ground, and means for selectively switching one of said transistors to a state of high conductivity and for maintaining the rest of said transistors in a state of low conductivity, whereby different fractions of said winding may be selectively connected to said load.

2. A switching circuit comprising a transformer having a primary winding and a secondary winding, said secondary winding being provided with a number of tap pings, a load connected directly from one of said tappings to ground, a plurality of transistors the emitter collector paths of which are connected directly from diflerent ones of said tappings to ground, and means for maintaining a selected one of said transistors in a state of high conductivity and the remainder of said transistors in a state of low conductivity, whereby there is applied to said load a proportion of a signal applied to said primary winding dependent on which transistor is selected.

3. A switching circuit comprising a tapped transformer winding, a load connected directly from one tapping of said Winding to ground, a plurality of transistors the emitter collector paths of which are connected directly from diiferent tappings of said winding to ground, and means for applying a first steady voltage to the base of a selected one of said transistors and a second steady voltage to the remainder of said transistors, said first steady voltage being such as to maintain said selected transistor in the conducting condition, and said second steady voltage said transistor.

References Cited by the Examiner UNITED STATES PATENTS 2,653,139 11/1953 Abate 235-154 3,019,426 1/1962 I Gilbert 235-154 3,023,405 4 2/1962 Scott 235-154 3,095,509 6/1963 Hileman et al 307-885 DAVID J. GALVIN, Primary Examiner. ARTHUR GAUSS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,246,174 April 12, 1966 Donald Ernest Tyzack It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, line 3, after "England; insert assignor to Electric G Musical Industries Limited, of Hayes, Middlesex, England, a company of Great Britain, line 12, for "Donald Ernest Tyzack, his heirs" read Electric G Musical Industries Limited, its successors and in the heading to the printed specification, lines 3 and 4, for "Donald Ernest Tyzack, "Spinelle," Narcot Lane, Chalfont St, Giles, England" read Donald Ernest Tyzack, Chalfont St. Giles, England, assignor to Electric G Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Signed and sealed this 5th day of September 1967.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Attesting Officer 

1. FIG-01
 1. A SWITCHING CIRCUIT COMPRISING A TAPPED TRANSFORMER WINDING, AN OUTPUT LOAD HAVING ONE TERMINAL CONNECTED DIRECTLY TO ONE TAPPING OF SAID WINDING AND HAVING A SECOND TERMINAL CONNECTED DIRECTLY TO GROUND, A PLURALITY OF TRANSISTORS THE EMITTER COLLECTOR PATH OF EACH OF WHICH IS CONNECTED DIRECTLY FROM A RESPECTIVE TAPPING OF SAID WINDING TO GROUND, AND MEANS FOR SELECTIVELY SWITCHING ONE OF SAID TRANSISTORS TO A STATE OF HIGH CONDUCTIVITY AND FOR MAINTAINING THE REST OF SAID TRANSISTORS IN A STATE OF LOW CONDUCTIVITY, WHEREBY DIFFERENT FRACTIONS OF SAID WINDING MAY BE SELECTIVELY CONNECTED TO SAID LOAD. 